U.S. Pat. No. 5,156,632 to Wellershaus discloses a jointless prosthetic foot having an S-shaped body. U.S. Pat. No. 6,197,066 to Gabourie discloses yet another one-piece prosthetic foot. It is configured for stop-limited dorsiflexion or dorsiflexion and plantarflexion. A C-shaped “ankle” section is provided that offers a hinge effect until the opening of the shape is closed. At this point, the remainder of the foot is said to be as stiff as possible to facilitate toe-off.
U.S. Pat. No. 5,139,525 to Kristinsson eschews such simplicity in favor of a highly complex mechanical action in which a J-shaped spring attached to a footbed portion includes a snubbing element within the curve of the spring to alter its spring rate. By internal contact of the snubber within the curvature of the spring, corresponding foreshortening of a lower free spring portion occurs to produce increased spring resistance to increased load on the prosthetic foot—and corresponding spring stresses. Such a spring element must be extremely robust.
The present invention bears only an outward resemblance to these designs by way of incorporating what might be seen (in some embodiments) as a J-shaped spring. However, the subject design is implemented in a multi-component construction that avoids features that would introduce problematic stressing leading to bulky spring elements. Accordingly, the present invention is unique in its high performance form and function.